I want to measure the cumlative power consumed by a single circuit over a period of time. I believe that devices like "Kill-A-Watt" can do this, but this is a 240v (40A) circuit. Is there a similar, inexpensive device for 240v? Also, is there anything that doesn't require a direct connection, that functions like a clamp-on ammeter? I can hard wire something in if necessary, but simple is good, too.